Prior fuel injection systems which may be used with, for example, diesel engines, have typically been of the pump-line-injector type or the unit injector type. A pump-line-injector fuel injection system includes a main pump which pressurizes fuel to a high level, e.g., on the order of about 103 to 138 MPa (about 15,000 to 20,000 p.s.i.), and individual fuel injectors which are coupled by fuel supply lines to the pump. In a unit injector system, a low-pressure transfer pump delivers fuel to a plurality of unit injectors, each of which includes means for pressurizing the fuel to a relatively high value, again on the order of about 103 to 138 MPa (15,000 to 20,000 p.s.i.) or greater.
Fuel injectors of the electronically-controlled unit injector type typically deliver fuel which is at a low pressure, for example, 60 p.s.i., to a pressure chamber and isolate the fuel within the pressure chamber using, for example, a spill control valve such as a poppet valve having a valve seating portion which comes into contact with a valve seat to isolate the pressure chamber from the fuel source. Alternatively, a spool valve may be used in place of a poppet valve. The fuel within the pressure chamber is then pressurized before being injected through a check valve into an engine combustion chamber. A spring forces the spill poppet valve of such a fuel injector against a stop so that the poppet valve is biased in an open position. Furthermore, a solenoid or other actuator controls the movement of the spill poppet valve assembly to force the valve seating portion into contact with the valve seat.
Fast actuation or deactivation of the solenoid, however, may cause the poppet valve to bounce or rebounce after an initial contact with the valve seat or stop. Bounce during closing of the poppet valve causes incomplete isolation of the fuel within the pressure chamber and slows the pressurization step of the fuel injection cycle resulting in lower engine thermal efficiency and higher exhaust emissions. If a bounce of great enough magnitude occurs during opening, the poppet valve can reseat against the valve seat causing pressurized fuel within the pressure chamber to create an undesired secondary injection of fuel into the engine combustion chambers.
It is known to dampen the movement of a valve within a fuel injector body. Trachte, et al., U.S. Pat. No. 4,605,171, issued on Aug. 12, 1986 for example, discloses a fuel injector which dampens the motion of a valve as the valve reciprocates within an injector body. During a fuel injection cycle, pressurized fuel within the injector body acts on an annular ring which is coupled to the valve to force the valve in an opening direction and thereby to cause fuel to be injected into an engine combustion chamber. As the valve moves in the opening direction, an end of the valve, which is disposed in a fuel filled damping chamber, moves out of the damping chamber to increase the volume of the damping chamber and, thereby, to decrease the pressure of the fuel within the damping chamber. The low pressure fuel within the damping chamber acts on the end of the valve to the damp the motion of the valve as the valve moves toward the open position. The damping chamber does not, however, prevent valve bounce when the valve reciprocates to the closed position.